Direct lifetime measurement of excited states in $^{72}$Ni

The long isotopic chain of nickel contains three doubly-magic isotopes $^{48}$Ni, $^{56}$Ni and $^{78}$Ni. The nuclei close to doubly magic systems with small number of valence nucleons can help in the understanding of shell closure effects, isomerism, and single particle states. The recent B(E2; 2$^+ \to$ 0$^+$) measurements at GANIL, and the 2$^+$ inelastic scattering cross-section measurements at NSCL, reveal unexpected collectivity in $^{70}$Ni and $^{74}$Ni. We measured electromagnetic transition rates in $^{72}$Ni using the recoil distance technique coupled with the improved gamma-ray detection array GRETINA with the NSCL/Koln plunger at the NSCL. The excited 2$^+_1$ and 4$^+_1$ in $^{72}$Ni states were populated by a one-proton knockout reaction of a $^{73}$Cu secondary beam on beryllium target. Lifetimes were obtained by comparing the measured spectra to simulated ones based on an existing code which utilizes GEANT4 with the geometry of the present setup.